Re: [quicwg/base-drafts] Remove the explicit packet number gap in favor of one computed (#496)

[janaiyengar <[e-mail]>]

janaiyengar commented on this pull request.



> @@ -1296,6 +1291,22 @@ connection ID, it should expect packets on the new connection ID to start at 18.
 A packet with the new connection ID and a packet number of 17 is discarded as
 being in error.
 
+#### Packet Number Gap
+
+In order to avoid linkage, the packet number gap MUST be externally
+indistinguishable from random. The packet number gap for a connection
+ID with sequence number is computed by encoding the sequence number
+as a 32-bit integer in big-endian format, and then computing:
+
+~~~
+Gap = HKDF-Expand-Label(packet_number_secret,
+                        "QUIC packet sequence gap", sequence, 4)

Why wouldn't a simple keyed-hash be adequate? Of course, organization of text shouldn't determine our design; do you have a suggestion for organizing the text if HKDF is to be used?

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